Practical 10.5 - Page 140 of 3rd Edition "Continuing Chemistry" - Anne Wignall & Terry Wales
This experiment involves being given 4 unknown substances labelled W, X, Y, and Z. Using a variety of laboratory substances to determine what functional group the organic substances contain. Any methods could be used, and the following are only a few of what methods were used in the entire class during the experiment.
The initial smell test gave an unpleasant (open to suggestion) smell. This gave us an indication that the substance may have been an amine or an aldehyde.
We added red litmus to the solution and the litmus turned blue. This showed an indication of a high pH and a concentration of OH- ions, or the ability to create OH- ions.
Therefore we came to the conclusion Product W is an amine.
Product X
The initial smell test gave a vinegar smell. This gave us an indication that the substance may have been a carboxylic acid or possibly a ketone.
We added blue litmus to the solution and the litmus turned red. This showed an indication of a low pH and a concentration of H+ ions, or the ability to create H+ ions.
Therefore we came to the conclusion Product X is a carboxylic acid.
The initial smell test gave a pleasant (again, open to suggestion) smell. This gave us an indication that the substance may have been a ketone or possibly an alcohol.
To test for an aldehyde, which was for some reason thrown into the mix of possible substances, we created Tollen's reagent, which had no reaction with Product Y. However, when tested with a known aldehyde - propanal, Tollen's reagent created a silvery mirror on the bottom inner surface of the test tube with a slightly evident black precipitate.
When adding water to the substance, we found that it was soluble. Esters are not miscible, and therefore we came to the conclusion Product Y is a ketone.
Product Y was presented to be a secondary alcohol. To test for this, Lucas reagent should have been used, and the solution would have turned cloudy when warmed over a long period of time.
(Unfortunately, video uploading crapped out here… I'll get onto that.)
Product Z
When water was added to this substance, two layers formed. Therefore the substance was insoluble. Insoluble substances include alkanes, alkenes, esters etc…
We added ammonium hydroxide to the solution to form an amine through nucleophilic substitution. To verify, we added red litmus to the new solution and it turned blue.
Therefore we came to the conclusion that Product Z is an alkene.
Product Z was presented to be an ester. To test for this, alcoholic ammonia can be added to form an amide and an alcohol. If the carbon chain is long enough, the amide could be found as a white precipitate at the bottom of the tube, as well as red litmus being added to the new solution turning blue.
I like how you explained what else you should have done with Solution Y to tell if it was a ketone or an alcohol, then to see that it was a secondary alcohol.
ReplyDeleteAgain, your reflection on analysing Solution Z was good. There are simpler tests to check if the solution is an ester or a hydrocarbon, though.